Method of manufacture of cathode ray tubes having frit-sealed envelope assemblies

ABSTRACT

A cathode ray tube envelope is flushed, soon after the faceplate panel is sealed to the funnel, with a non-contaminating gas, such as nitrogen or warm air, to remove any contaminating materials that may have been produced therein during the sealing operation, and a filling of the gas is maintained in the envelope until the latter is exhausted and sealed off, whereby the envelope can be held or stored for a relatively long period between the sealing and exhaust steps without appreciably reducing the life of the completed tube.

United States Patent n51 3,658,40 1 Files [4 1 Apr. 25, 1972 [54] METHOD OF MANUFACTURE OF 2,520,190 8/1950 CATHODE RAY TUBES HAVING FRIT- 5.233% 5:323 SEALED ENVELOPE ASSEMBLIES 5 5 I 6/1968 [72] inventor: John Austin Files, Amboy, lnd. 3,432,712 3/1969 [73] Assign: RCA Corporation Primary Examiner-John F. Campbell [22] Filed: Jan. 6, 1970 Assistant Examiner-Richard Bernard Lazarus pp NO 959 Attorney-Glenn H. Bruestle ABSTRACT [52] US. Cl ..3l6/2l, 316/20, glitz/2245; A cathode my tube envelope is flushed. soon after the faceplate panel is sealed to the funnel, with a non-contaminatga 8 G ing gas, such as nitrogen or warm air, to remove any con. 5 g taminating materials that may have been produced therein during the sealing operation, and a filling of the gas is maintained in the envelope until the latter is exhausted and sealed [56] Rehrences and off, whereby the envelope can be held or stored for a relatively UNITED s ATES p ATENTS long period between the sealing and exhaust steps without appreciably reducing the life of the completed tube. 2,091,863 8/1937 Kessler ..3l6/I9 2,334,718 I l/l943 Lowry et al ..3 I 6/21 6 Claims, 5 Drawing Figures FRIT SEAL PANEL TO FUNNEL TO, FORM ENVELOPE IMMEDIATELYADMIT NON- CONTAMINATING GAS TO FLUSH RESIDUAL ATMOSPHERE AND FILL ENVELOPE MAINTAIN ENVELOPE FILLING DURING A HOLD PERIOD INSERT AND MOUNT ELECTRON GUN AND GETTER PERFORM CONVENTIONAL F CATHODE ACTIVATION,TIP-OFF,

GETTER FLASH, ETC.

I PATENTEDAPR 25 I972 SIIEET 1 DE 2 FRIT SEAL PANEL TO FUNNEL TO FORM ENVELOPE IMMEDIATELY ADMIT NON- CONTAMINATING GAS TO FLUSH RESIDUAL ATMOSPHERE AND FILL ENVELOPE MAINTAIN ENVELOPE FILLING DURING A HOLD PERIOD INSERT AND MOUNT ELECTRON GUN AND GETTER EXHAUST AND BAKE TO REMOVE GAS FILLING AND DE-GAS ELECTRODES Fig.1.

INVEN'IURI John 4. Files AGE/VT .JAmaKM/M PATENTEU APR 2 s 1972 SHEET 2 BF 2 Fig. 5.

INVFNFOR B John (1A. files 94mm 1?. w

AGENT METHOD OF MANUFACTURE OF CATHODE RAY TUBES HAVING FRIT- SEALED ENVELOPE ASSEMBLIES BACKGROUND OF THE INVENTION The present invention relates to an improvement in the manufacture of a cathode ray tube having an envelope or bulb comprising a faceplate panel frit-sealed to a funnel. An example of such a cathode ray tube is the well-known shadow mask type of color picture tube, wherein a color selection shadow mask is mounted in a faceplate panel adjacent to the faceplate, the color phosphor screen is produced on the faceplate by a photographic process using the mask as a stencil, and the completed panel is sealed to a separate funnel to form the envelope.

The seal between the panel and funnel is usually made by forming a bead of devitrifiable glass frit on the mating edge of one of the parts, by applying a suspension or slurry of a special powdered glass mixed with an organic binder and vehicle, assembling the two parts, and placing the assembly in an oven or lehr having a maximum temperature between 400 and 500 C., to devitrify and harden the frit, as disclosed in Claypoole U.'S. Pat. No. 2,889,952, dated June 9, 1959.

After the frit-seal is made, the envelope is subjected to various operations, including insertion and mounting of the electron gun and getter in the funnel, cathode activation, bake and exhaust to remove most of the gas and other impurities, tipoff, getter flash, and ageing. The function of the getter is to chemically or physically sorb residual gases present or produced within the envelope during the life of the cathode ray tube. The tube life is largely dependent upon the getter sorption capacity," or. the capability of the getter to sorb gases. Two factors of importance are (l) the initial getter sorption capacity, and (2) the rate of depletion of getter sorption capacity (e.g. per hour) during tube life.

Sample completed color tubes are constantly being lifetested to determine the effects of various factors on tube life. The normal time between frit-seal and exhaust is about 2 hours, including about 1 hour between frit-seal and gun insertion. It has been known for several years that color tubes made from envelopes that were held or stored for a substantially longer period of time (e.g. more than 8 hours) after frit-seal before exhaust, capped or uncapped, exhibited much higher rate of depletion of getter sorption capacity during life than tubes made from envelopes that were processed soon after frit seal, with no substantial hold period prior to exhaust, even though the initial getter sorption capacities of the held tubes were nearly as high as those of tubes not held. The reason for this condition was previously unknown. Since the condition existed for capped as well as uncapped envelopes, it did not appear to be caused by the entry of air into the envelope after frit-seal. On the other hand, if the condition were caused by the residual atmosphere in the envelope at frit-seal, why was it not eliminated by the subsequent exhaust and bake operation? For many years, it has been known in the art of rebuilding cathode ray tubes that the bake-out operation during exhaust of a re gunned tube could be eliminated by filling the tube envelope with a non-contaminating gas, such as nitrogen or air, when the neck is cracked off, and maintaining the gas therein throughout the re-gunning operation, to prevent contamination of the internal parts of the tube by air, as disclosed in Trax US. Pat. No. 3,063,777 dated Nov. 13, 1962. However, this process has not been suggested, or used, prior to the present invention, for new cathode ray tubes following the envelope sealing operation.

SUMMARY OF THE INVENTION residual atmosphere in the envelope at frit-seal, if left in the envelope for sufficient time, contaminates the envelope and/or contents permanently, so that the condition cannot be eliminated by subsequent bakeout and exhaust. I also realized that if this were true, it might be possible to eliminate or at least minimize this contamination, and thereby improve the tube life, by flushing the residual gas from the envelope soon after frit-seal with a non-contaminating gas. Comparative life tests, on (1) color tubes flushed soon after frit-seal and then held for periods of up to three weeks before exhaust, and other tubes that were either 2) held without flushing between operations or (3) processed soon after frit-seal without either flushing or holding, showed clearly that the flushed and held tubes had nearly as low rates of depletion of getter sorption capacities during life as tubes that were not held at all, and not more than about half of the rates of tubes that were held without flushing.

It is not known exactly how the residual atmosphere in the envelope at frit-seal contaminates the envelope to produce the condition described. The contaminating materials appear to be organic and/or inorganic materials, including hydrocarbons, carbon dioxide and water vapor, produced in the fritseal process itself. It appears that, when the envelope is held for a relatively long period after frit-seal and before exhaust, these materials become combined with the internal surfaces of the envelope, mask or screen to such an extent that they cannot be removed (completely) during the normal exhaust and bake operation. The water vapor may hydrolize the silicate binder for the graphite funnel coating and produce materials which combine with hydrocarbons and/or carbon dioxide from the frit seal to produce stable oxygen-containing compounds. These compounds may be broken down during tube operation, by electron bombardment and/or other causes, and produce gases which cause a large increase in the rate of depletion of the getter sorption capacity, which greatly reduces the operating life of the tube.

The envelope may be flushed with any dry non-contaminating gas, such as nitrogen or warm air. After flushing, the envelope may be temporarily closed, by capping or plugging, to maintain a non-contaminating gas filling therein during a subsequent hold period prior to gun insertion and exhaust.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a flow-chart showing a method comprising the invention.

FIG. 2 is a side view of a cathode ray tube envelope with gas flushing apparatus.

FIG. 3 is an enlarged detail of a portion of the flushing tubing of FIG. 2.

FIG. 4 is an enlarged axial sectional view of a portion of the tube neck in FIG. 2.

FIG. 5 is a side view of a tube envelope capped off for bolding or storage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The steps A through F of a method comprising the inventions are shown in the flow-chart of FIG. I. A glass panel may be frit-sealed to a glass funnel, in step A, by the method described in Claypoole US. Pat. No. 2,889,952 to form the tube envelope. Prior to frit-seal, the mask assembly has been mounted in the panel, the faceplate has been screened, aluminized and baked, and the funnel has been provided with its internal conducting (graphite) coating. The funnel is made up of a cone portion sealed at its larger end to the panel and a cylindrical neck portion joined to a smaller end of the cone and having its other end open to receive the tube stem and electron gun.

In accordance with the invention, shortly after it leaves the frit-seal lehr, the envelope is processed to flush the residual atmosphere therefrom and fill it with a non-contaminating gas, step B. This may be done, as shown in FIGS. 2-4, by inserting an elongated tubing 1 and a surrounding resilient stopper 3 into the open end of the neck 5 of a color tube envelope 7 and admitting the gas from a gas source 9 through a valve I0 and the tubing 1. The upper end of the tubing 1 may be formed with apertures 11 for directing the gas in a desired manner, e.g., outwardly. The outer periphery of the stopper 3 is either non-circular or formed with longitudinal grooves 13 to permit the residual gases within the envelope to be flushed out of the envelope by the gas from source 9. Instead of centering the tubing 1 axially with respect to the stopper 3, as shown in FIG. 4, the tubing 1 may be eccentric to the stopper to improve the flushing action. It will be understood that the size of the tubing 1, apertures 11 and grooves 13 and the gas pressure of the source 9 should be chosen to produce the desired flushing time. In one apparatus that has been used successfully in making 25 inch rectangular color tubes, the envelope is flushed for approximately 1 minute, and the volume is exchanged a minimum of 3 times.

The non-contaminating gas is preferably dry warm air having a dew point of about 30 C., in order to minimize the water vapor present. However, water vapor alone, without hydrocarbons and carbon dioxide, does not appear to produce contamination, and hence, the hydrocarbons and carbon dioxide, and other contaminants, if any, can be satisfactorily flushed out with air (or nitrogen) at room temperature, having a dew point as high as C. Satisfactory tubes have been made experimentally using room temperature air having a dew point of 1 6 C.

Preferably, the envelope is flushed within minutes after it leaves the fritseal lehr, to minimize contamination. However, since the contamination is a slow process, this time is not critical, and can be as long as a few hours. It appears that very little contamination occurs within the first hour after frit-seal.

After the flushing is completed, the flushing apparatus is removed, and may be replaced by a temporary closure, such as the resilient cap 15 shown in FIG. 5, to maintain the envelope 7 filled with the non-contaminating gas at atmospheric pressure for a relatively long hold period prior to the next manufacturing operation, which is usually combined gun-insertion and stem-sealing (step C). It has been found that envelopes so flushed and capped can be held or stored up to 3 weeks, if necessary or desired, without causing a large increase in the normal rate of depletion of getter sorption capacity during tube life after manufacture.

If the envelope is to be moved soon, to the gun-insertion and stem-sealing apparatus, the capping of the flushed envelope may be omitted, since the rate of diffusion of gases into and out ofthe open neck is small.

Although the flushing operation is not essential unless the envelope is held substantially longer than the normal two hours between frit-seal and exhaust, incorporation .of the flushing operation in the manufacture of all color tubes manufactured by applicant's assignee is planned, in order to insure that all color tubes manufactured will have adequate gettering capacity during life, whether or not they are held for a period during manufacture.

In step D, the electron gun and getter may be inserted in the neck 5, and the glass stem (on which the gun is mounted) sealed to the open end of the neck by known methods, e.g., as shown in FIG. 5 of Trax US. Pat. No. 3,063,777. The getter is normally supported on the electron gun and positioned either adjacent to the end of the gun or within the cone portion of the funnel.

The envelope may be exhausted and baked in step E, to remove the gas filling introduced by step B, and to de-gas the various electrodes and other internal surfaces, by any known method, e.g., as described in Johnson et al. US. Pat. No. 2,532,3 l5,dated Dec. 5, 1950.

After exhaust, the manufacture of the color tube is completed by performing the conventional steps of activation of the cathodes, tip-off of the exhaust tubulation, flashing of the getter to produce a gas absorbing coating of getter material (e.g., barium) on the interior surfaces of the tube, ageing of the gun electrodes, and testing, collectively referred to as step F in FIG. 1.

A series of life tests on 1. Five color tubes that were flushed after frit-seal and held for periods of l, 2 and 3 days before exhaust; and

2. Five tubes that were held without flushing after frit-seal for similar periods before exhaust, produced the following results. The average oxygen gas capacity of the getters in the five tubes in group (1) at the end of l 1 weeks was 5352 111. (liter-microns), as compared to an average of 2704 1 1. at l 1 weeks for the five tubes in group (2). Thus, the flushing of the first group of held tubes doubled the average capacity at 1 1 weeks, and hence, greatly increased the potential life of those tubes. Moreover, the average gas capacity of the getters in group (1) was not substantially less than that of a standard color tube manufactured without flushing or holding.

I claim:

I. In the manufacture of cathode ray tubes each having an envelope comprising a faceplate panel frit-sealed to a funnel; each of said envelopes containing an electron gun, and a getter adapted to absorb gases during the life of the tube; the method comprising the steps of:

a. frit-sealing said panels to said funnels to form said envelopes by a process resulting in the production of contaminating materials within said envelopes;

b. flushing each of said envelopes soon after said frit-sealing step with a non-contaminating gas to remove said contaminating materials and fill said envelope with said gas;

c. maintaining said gas in said envelopes until exhaust;

d. inserting and mounting an electron gun and a getter within each of said envelopes; and

e. then exhausting and sealing off each of said envelopes to remove said gas and complete said tube; whereby one or more of said envelopes can be held for a period of time between said frit-sealing and said exhausting steps sufiicient to make the total elapsed time between said steps substantially greater than the normal time without a hold, without substantially reducing the useful life of said getter during subsequent tube operation.

2. The method of claim 4, wherein each of said envelopes is flushed in steps (b) within I hour after the completion of sealing step (a).

3. The method of claim 4, wherein said non-contaminating gas has a dew point not greater than 0 C.

4. The method of claim 1, wherein each of said envelopes is temporarily closed at the end of step (b) to maintain said gas within said envelope.

5. In the manufacture of a cathode ray tube having an envelope comprising a faceplate panel frit-sealed to a funnel, said envelope containing an electron gun, and a getter adapted to absorb gases during the life of the tube; the method com prising the steps of:

a. frit-sealing said panel to said funnel to form said envelope by a process resulting in the production of contaminating materials within said envelope;

b. flushing said envelope soon after said frit-sealing step with a non-contaminating gas to remove said contaminating materials and fill said envelope with said gas;

c. maintaining said gas in said envelope until exhaust;

d. inserting and mounting an electron gun and a getter within said envelope;

e. holding said envelope for a period of time sufficient to make the total elapsed time between frit-sealing and exhaust substantially greater than the normal time without a hold; and then exhausting and sealing off said envelope to remove said gas and complete said tube; so that said holding will not substantially reduce the useful life of said getter during subsequent tube operation.

6. In the manufacture of cathode ray tubes each having an envelope comprising a faceplate panel frit-sealed to a funnel; each envelope containing an electron gun, and a getter adapted to absorb gases during the life of the tube; the method comprising the steps of:

e. holding one or more of said envelopes for periods of time sufi'icient to make the total elapsed time between frit-seal and exhaust substantially greater than the normal time without a hold; and

t. then exhausting and sealing off each of said envelopes to remove said gas and complete said tube; so that said holding will not substantially reduce the useful life of said getter during subsequent tube operation.

il I! t t 4 

1. In the manufacture of cathode ray tubes each having an envelope comprising a faceplate panel frit-sealed to a funnel; each of said envelopes containing an electron gun, and a getter adapted to absorb gases during the life of the tube; the method comprising the steps of: a. frit-sealing said panels to said funnels to form said envelopes by a process resulting in the production of contaminating materials within said envelopes; b. flushing each of said envelopes soon after said frit-sealing step with a non-contaminating gas to remove said contaminating materials and fill said envelope with said gas; c. maintaining said gas in said envelopes until exhaust; d. inserting and mounting an electron gun and a getter within each of said envelopes; and e. then exhausting and sealing off each of said envelopes to remove said gas and complete said tube; whereby one or more of said envelopes can be held for a period of time between said frit-sealing and said exhausting steps sufficient to make the total elapsed time between said steps substantially greater than the normal time without a hold, without substantially reducing the useful life of said getter during subsequent tube operation.
 2. The method of claim 4, wherein each of said envelopes is flushed in steps (b) within 1 hour after the completion of sealing step (a).
 3. The method of claim 4, wherein said non-contaminating gas has a dew point not greater than 0* C.
 4. The method of claim 1, wherein each of said envelopes is temporariLy closed at the end of step (b) to maintain said gas within said envelope.
 5. In the manufacture of a cathode ray tube having an envelope comprising a faceplate panel frit-sealed to a funnel, said envelope containing an electron gun, and a getter adapted to absorb gases during the life of the tube; the method comprising the steps of: a. frit-sealing said panel to said funnel to form said envelope by a process resulting in the production of contaminating materials within said envelope; b. flushing said envelope soon after said frit-sealing step with a non-contaminating gas to remove said contaminating materials and fill said envelope with said gas; c. maintaining said gas in said envelope until exhaust; d. inserting and mounting an electron gun and a getter within said envelope; e. holding said envelope for a period of time sufficient to make the total elapsed time between frit-sealing and exhaust substantially greater than the normal time without a hold; and f. then exhausting and sealing off said envelope to remove said gas and complete said tube; so that said holding will not substantially reduce the useful life of said getter during subsequent tube operation.
 6. In the manufacture of cathode ray tubes each having an envelope comprising a faceplate panel frit-sealed to a funnel; each envelope containing an electron gun, and a getter adapted to absorb gases during the life of the tube; the method comprising the steps of: a. frit-sealing said panels to said funnels to form said envelopes by a process resulting in the production of contaminating materials within said envelopes; b. flushing each of said envelopes soon after said frit-sealing step with a non-contaminating gas to remove said contaminating materials and fill said envelope with said gas; c. maintaining said gas in said envelopes until exhaust; d. inserting and mounting an electron gun and getter within each of said envelopes; e. holding one or more of said envelopes for periods of time sufficient to make the total elapsed time between frit-seal and exhaust substantially greater than the normal time without a hold; and f. then exhausting and sealing off each of said envelopes to remove said gas and complete said tube; so that said holding will not substantially reduce the useful life of said getter during subsequent tube operation. 